JPS5967445A - Humidity sensor - Google Patents

Abstract

PURPOSE:To measure the humidity with a high sensitivity utilizing strain of a gauge due to humidity variation by forming a strain gauge resistance pattern on an elastic insulation substrate with a small hygroscopicity and an organic humidity-sensitive thin film on the pattern surface by plasma polymerization. CONSTITUTION:A strain gauge pattern 2 made of a copper nickel alloy or the like varying in the electric resistance value subject to a strain is formed on one side of an elastic insulation substrate 1 with a small hygroscopicity made of a plastic film and a connection leader 3 is mounted. Substrates 1 and 1 thus obtained are stuck togehter so as to have strain gauge resistances 2 and 2' on both sides thereof. Protective covers 4 and 4 are applied on the respective resistances 2 and 2' and then, a thin humidity sensitive film 5 is formed on one cover 4 by plasma polymerization of a nitrogen-containing monomer such as aryl amine to make a humidity sensor. The film 5 detects changes in the electric resistance of the gauge resistances 2 and 2' caused expanding according to the humidity in the atmosphere. Thus, a sensor with a better response and a higher durability is obtained.

Description

[Detailed description of the invention] The 6th book will be about humidity sensors.

Its purpose is to create a humidity sensor that combines a humidity sensing part and a detection part independently. It can detect changes in humidity directly as an electrical signal, has excellent responsiveness, and can quickly measure humidity. It is also affected by atmospheric gases in the pond.
``Our goal is to develop a new, multi-piece humidity sensor that is highly durable, suitable for mass production, and can be produced at low cost.''

Hair-type sensing means and wet-bulb sensing means, which have been used in hygrometers for a long time, have the disadvantage of slow response to changes in humidity. Electrical conductivity and electrostatic silkworm quantity (
Humidity sensors that extract changes in humidity as electrical signals have been developed, and hygrometers, dew point meters, etc. using these sensors have become commercially available.

Surrounding gases, especially carbon dioxide, sulfur dioxide, and silicon dioxide, have the disadvantage of being affected by gases that ionize when wet, which can easily cause disturbances in electrical signals, and they are also susceptible to dust, etc. However, the responsiveness of the capacitance is also not satisfactory, and some methods based on direct changes in capacitance have manufacturing difficulties, such as requiring the extraction electrode to be formed on the moisture-sensitive membrane. It had various problems such as.

The inventor of the present invention kept the above points in mind, focused on the fact that a resistance type strain gauge causes a change in resistance value during bending deformation, and as a result of diligent research, the inventor combined a moisture-sensitive film and this strain gauge to form a moisture-sensing section. He invented a humidity sensor with an independent detection section.

The invention is to provide a strain gauge with a strain gauge resistance pattern formed on an insulating substrate with low hygroscopicity and full elasticity, and a moisture sensitive film of an organic thin film deposited by plasma polymerization reaction on the surface of the pattern. The humidity sensor is characterized in that it detects the amount of warpage caused by the difference in expansion coefficient during moisture absorption and desorption between the moisture sensitive film and the insulating substrate as a resistance (surface change) of the strain gauge. It is something to do.

The present invention will be explained with reference to the drawings.

FIG. 1 is an enlarged front view 1 showing an example of a strain gauge used in the sensor of the present invention.

As shown in this figure, the strain gauge (a) used in the invention has a gauge resistor (2) formed as an S-turn on one side of an insulating substrate (1).

This insulating substrate (1) must be made of a material with low hygroscopicity and elasticity, such as a glass film, an extremely thin glass plate, a ceramic plate, or a metal plate with an insulation treatment applied to the surface. It can be used.

Also, a pattern is provided on one side of this insulating substrate (1).
The gauge resistor (2J Id:, ) may be made of various known metals, alloys, etc. whose electrical resistance value changes when bent; for example, steel-nickel alloy is a suitable material. .

Note that (3) in FIG. 1 is a connecting lead line.

Figure 2 is an enlarged side cross-sectional view 1 of one embodiment of the sensor of the present invention.
It is.

The sensor of the present invention, for example, uses two of the above-mentioned strain gauges (AT) and adheres the insulating substrates (1) to each other, and a gauge resistor (2) (2'l) is installed on both sides of the sensor. After that, a gauge protective film (4) is provided on the other side of the gauge resistor (2), and a moisture-sensitive film (A-type thin film) is formed on only one side of the gauge resistor (2) by a thin film forming means using a plasma polymerization reaction.
5] is coated with a film.

The embodiment shown in this figure combines two strain gauges (a), has a gauge resistor (21) on both sides, and only one of them has a moisture-sensitive film (b) by a plasma reaction It is forming.

This plasma-polymerized moisture-sensitive film (5) is an organic thin film that exhibits the remarkable property of expanding upon absorption of moisture, shortening upon dehumidification, and returning to its original state.For example, allylamine polymer,
Acrylamide polymer, acrylonitrile polymer,
Organic thin films obtained by plasma polymerization of 1i element-containing monomers, such as Ta.

The thickness of this moisture-sensitive film (5) is extremely thin, for example, the thickness of the plasma-polymerized allylamine film described above is 1000 to 5000.
It can be made with a thickness of λ, and because it is an extremely thin piece, it absorbs and extracts moisture quickly and becomes a humidity sensor with excellent responsiveness.

FIG. 3 is an enlarged side cross-sectional view (see 1) showing how the embodiment shown in FIG. 2 absorbs moisture and warps.

As shown in this figure, even if the moisture-sensitive membrane (5) absorbs moisture and expands greatly, the insulating substrate (1) hardly absorbs moisture, so the expansion is slight, and due to this difference in expansion rate, this sensor ) side is on the inside, which means the moisture-sensitive membrane (May rule) is on the outside and bends.

As a result, the electrical resistance value of the inner gauge resistor (2') decreases, and the electrical resistance of the outer gauge resistor (2) increases. This decrease in resistance value 'J''tl naturally changes depending on the degree of warpage of this sensor, and this degree of warpage is determined by the degree of moisture absorption of the moisture sensitive film (5).

In other words, the expansion and contraction of the moisture-sensitive membrane (5J) due to moisture absorption and desorption causes a warpage change in the strain gauge (a), which can be detected as an electrical signal called a change in the gauge resistance.

As explained above, the present invention is a humidity sensor that combines a strain gauge and a moisture-sensitive membrane, in which a moisture-sensitive membrane that expands and contracts depending on humidity and a detection section that extracts this as a change in resistance lit are integrated independently of each other. This is a completely new technical idea, and since it directly converts humidity into an electrical signal regardless of the electrical properties of the moisture-sensitive membrane, its structure is extremely unaffected by surrounding air gas or dirt, and the detection part is highly reliable. The cut, 1, and peach also become excellent.

In fact, the sensor of the present invention has fewer troubles in manufacturing because the strain gauge part and the moisture sensing part do not affect each other in terms of characteristics, and the plasma reaction device in thin film technology uses IT to form the humidity sensitive film.・The production process is the same as that of conventional technology, the reproducibility is good, and the film thickness can be set arbitrarily, making it extremely easy to mass-produce and making it possible to produce inexpensive humidity sensors. It is.

As mentioned above, the sensor of the present invention has an extremely thin moisture-sensitive film, so it has a fast moisture absorption and desorption rate and can achieve humidity detection with excellent responsiveness.As described above, the sensor of the present invention has various effects and It is something that exhibits the lunar nature.

Example A Mylar film with a thickness of 50 μm was used as the insulating substrate (1), a gauge pattern of copper-nickel alloy was formed as the gauge resistor (2), and a protective film (4 ml) was placed on the surface of the gauge pattern.
) are in contact with each other, prepare two strain gauges (a), and
A double-sided strain gauge was created by bonding two insulating substrates (1) with an adhesive.

Next, a moisture sensitive film (5) having a film thickness of 3000λ is formed on one side of the double-toothed strain gauge by depositing allylamine while polymerizing it in a plasma polymerization reaction thin film forming device, thereby forming a humidity sensor of the present invention as shown in the second example. was produced.

A detection circuit as shown in FIG. 4 was created by combining two of these humidity sensors.

The deflection detection circuit is a full-bridge circuit consisting of four gauge resistors (120 units), and the gauge output is four times that of a single gauge, and it is also possible to correct drift due to changes in deflection.

Note that R1 and R2 in the figure indicate the gauge resistance within one humidity sensor, and RJ and R4 indicate the gauge resistance within the capacity humidity sensor. In other words, when moisture is absorbed, R1 and R3
indicates an increase in resistance, and R2 and R4 indicate a decrease in resistance.
The opposite is true during dehumidification.

P in Figure 4 represents the amplifier and recorder, where the sensor output is detected.

When this detection circuit was used to examine the relationship between relative humidity (RH) and sensor output (llV), the results shown in FIG. 5 were obtained.

In addition, the humidity fixed point of the salt-saturated bathing liquid in each building was used for the humidity measurement.

As shown in Fig. 5, the change from 0 coefficient RH to 98 coefficient RH'j was a curve with a slightly large slope on the low humidity side and a small slope on the humidity side, but it was clear that the sensor was not able to detect humidity changes. This can be interpreted as a change in output.

In addition, the response speed during this measurement is extremely fast at 10 to 20 seconds when absorbing moisture, and 40 to 60 seconds when dehumidifying, which is slightly slower than when absorbing moisture, so it responds within 7 seconds, compared to conventional products. It was concluded that the response was quite fast. Note that this response speed can be further reduced by using an insulating substrate that is less hygroscopic.

Furthermore, when the above sensor was examined at the same humidity for the influence of atmospheric gas (mainly the concentration of carbon dioxide), it was found that the sensor output did not change much.

[Brief explanation of drawings]

FIG. 1 is an enlarged front view showing an example of a strain gauge used in the sensor of the present invention. FIG. 2 is an enlarged side sectional view of one embodiment of the sensor of the present invention. FIG. 3 is an enlarged side sectional view showing how the embodiment shown in FIG. 2 absorbs moisture and warps. (1)...Insulating substrate, (2)...Gauge resistance, (3
)... Connection lead wire, (a)... Strain gauge consisting of (1), (2), and (3), (4)... Gauge protection film, (5)...
FIG. 4 is a detection circuit diagram in an embodiment of the present invention. Fig. 5 is a graph showing the relationship between the relative humidity (RH) determined by the detection circuit shown in Fig. 4 and the sensor output (μV).

Claims (1)

[Claims] 1. A strain gauge in which a strain gauge resistance pattern is formed on an insulating substrate with low hygroscopicity and elasticity, and a film is deposited on the surface of the pattern by a plasma polymerization reaction. A thin moisture-sensitive film is provided, and warpage caused by a difference in expansion coefficient during moisture absorption and desorption between the humidity-sensitive film and the insulating substrate is detected as a change in the resistance (i!) of the strain gauge. Patented humidity sensor. 2. The humidity sensor according to claim 1, wherein the moisture-sensitive film made of a thin organic material is a plasma-contained thin film of allylamine.